Ferro-taramite
Chemical formula: Na(NaCa)Fe²⁺₃Al₂(Si₆Al₂)O₂₂(OH)₂
Ferro-taramite is a rare, dark green to black sodium-calcium amphibole, occurring as prismatic crystals in metamorphic rocks.
Properties
- Mohs hardness
- 5-6
- Color
- Bluish green
- Luster
- Vitreous
- Streak
- Greenish-gray
- Density
- 0
- Cleavage
- {110} rather poor.
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Ferro-taramite is identified by its dark green to black color, prismatic crystal habit, and occurrence in metamorphic rocks. Characteristic of amphiboles is the cleavage angle (approximately 124°) between cleavage planes, visible in cross-sections of crystals. ## Distinguishing from Similar Minerals It can be confused with other dark amphiboles, such as hornblende or arfvedsonite, as well as pyroxenes (e.g., augite). It is distinguished from pyroxenes primarily by the cleavage angle (for pyroxenes, it is approximately 90°). Accurate identification and differentiation from other sodium-calcium amphiboles often require advanced chemical analyses (e.g., electron microprobe). ## Crystal Forms Crystals are typically elongated, prismatic, with a hexagonal cross-section. They often form radiating, granular, or fibrous aggregates. Well-formed, isolated crystals are rare.
Geological environment
## Genesis Ferro-taramite is a mineral characteristic of metamorphic rocks that have undergone transformation under conditions of medium to high pressures and temperatures. It forms mainly in amphibolites, glaucophane schists, and eclogites. It can also occur in some basic igneous rocks. ## Mineral Associations It often coexists with other metamorphic minerals, such as garnet (especially almandine), epidote, glaucophane, omphacite, rutile, quartz, and other amphiboles. ## Localities The most important localities from which well-studied ferro-taramite specimens originate include the Sesia area in Piedmont, Italy (type locality), as well as the Zermatt-Saas metamorphic complex in the Alps. Occurrences have also been reported in Greece (Sifnos island), Japan, and the United States.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, sharply terminated crystals with a distinct luster. Contrast with the rock matrix and the presence of associated minerals, such as pink or red garnet, are important. Crystal size is also a significant factor – larger, well-formed prisms are much rarer and more desirable. ## Popular Localities The best localities for this mineral are considered to be in the Alps, especially in Italy (Aosta Valley, Piedmont), from where classic specimens originate. Specimens from these localities often feature attractive associations with other metamorphic minerals.
Care and storage
## Cleaning Ferro-taramite specimens can be cleaned with a soft, dry brush to remove dust. If necessary, distilled water may be used, but prolonged soaking should be avoided. After wet cleaning, the specimen should be thoroughly dried. ## What to Avoid Contact with strong acids and bases, which can damage the mineral's surface, should be avoided. Ferro-taramite is relatively stable, but it should be protected from sudden temperature changes and strong, prolonged sunlight, which can lead to fading. ## Storage Specimens should be stored in stable conditions, away from dust and moisture. It is best to place them in closed display boxes or cabinets. Due to its moderate hardness, contact with harder minerals (e.g., quartz) should be avoided to prevent scratches.